[ELF][Writer] Add .interp section.

llvm-svn: 175657

lld/include/lld/ReaderWriter/ELFTargetInfo.h

@@ -49,6 +49,10 @@ public:
     return false;
   }
 
+  virtual StringRef getInterpreter() const {
+    return "/lib64/ld-linux-x86-64.so.2";
+  }
+
   /// \brief Does the output have dynamic sections.
   bool isDynamic() const {
     return _options._outputKind == OutputKind::DynamicExecutable ||

lld/lib/ReaderWriter/ELF/HeaderChunks.h

@@ -183,7 +183,8 @@ bool ProgramHeader<ELFT>::addSegment(Segment<ELFT> *segment) {
   for (auto slice : segment->slices()) {
     // If we have a TLS segment, emit a LOAD first.
     if (segment->segmentType() == llvm::ELF::PT_TLS ||
-        segment->segmentType() == llvm::ELF::PT_DYNAMIC) {
+        segment->segmentType() == llvm::ELF::PT_DYNAMIC ||
+        segment->segmentType() == llvm::ELF::PT_INTERP) {
       auto phdr = allocateProgramHeader();
       if (phdr.second)
         allocatedNew = true;

lld/lib/ReaderWriter/ELF/SectionChunks.h

@@ -758,6 +758,31 @@ public:
 private:
   EntriesT _entries;
 };
+
+template <class ELFT> class InterpSection : public Section<ELFT> {
+public:
+  InterpSection(const ELFTargetInfo &ti, StringRef str, int32_t order,
+                StringRef interp)
+      : Section<ELFT>(ti, str),
+        _interp(interp){
+    this->setOrder(order);
+    this->_align2 = 1;
+    // + 1 for null term.
+    this->_fsize = interp.size() + 1;
+    this->_msize = this->_fsize;
+    this->_type = SHT_PROGBITS;
+    this->_flags = SHF_ALLOC;
+  }
+
+  void write(ELFWriter *writer, llvm::FileOutputBuffer &buffer) {
+    uint8_t *chunkBuffer = buffer.getBufferStart();
+    uint8_t *dest = chunkBuffer + this->fileOffset();
+    std::memcpy(dest, _interp.data(), _interp.size());
+  }
+
+private:
+  StringRef _interp;
+};
 } // end namespace elf
 } // end namespace lld
 

lld/lib/ReaderWriter/ELF/Writer.cpp

@@ -69,6 +69,7 @@ private:
   /// \name Dynamic sections.
   /// @{
   LLD_UNIQUE_BUMP_PTR(DynamicTable<ELFT>) _dynamicTable;
+  LLD_UNIQUE_BUMP_PTR(InterpSection<ELFT>) _interpSection;
   /// @}
   CRuntimeFile<ELFT> _runtimeFile;
 };
@@ -337,7 +338,11 @@ void ExecutableWriter<ELFT>::createDefaultSections() {
   if (_targetInfo.isDynamic()) {
     _dynamicTable.reset(new (_alloc) DynamicTable<ELFT>(
         _targetInfo, ".dynamic", DefaultLayout<ELFT>::ORDER_DYNAMIC));
+    _interpSection.reset(new (_alloc) InterpSection<ELFT>(
+        _targetInfo, ".interp", DefaultLayout<ELFT>::ORDER_INTERP,
+        _targetInfo.getInterpreter()));
     _layout->addSection(_dynamicTable.get());
+    _layout->addSection(_interpSection.get());
   }
 
   // give a chance for the target to add sections

lld/test/elf/dynamic-interp.test

@@ -0,0 +1,8 @@
+RUN: lld -core -target x86_64-linux %p/Inputs/use-shared.x86-64 \
+RUN:   %p/Inputs/shared.so-x86-64 -output=%t -entry=main \
+RUN:   -output-type=dynamic
+RUN: llvm-objdump -p %t | FileCheck %s
+
+CHECK: INTERP
+CHECK: flags r--
+CHECK: off